Heat treated, hardened alloy steel elements



States atent 2,70s,1ss

HEAT TREATED, HARDENED ALLOY STEEL ELEMENTS Francis E. Foley,Philadelphia, Pa., and Charles (3. Clark, Little Falls, N. 3., assignorsto The International Nickel Company, Inc, New York, N. Y., a corporationof Delaware No Drawing. Application February 26, 1954, Serial No.412,942

6 Claims. (Cl. '75124) The present invention relates to hard machineelements, such as gears, dies, and the like, which are required to haveaccurate dimensions in the hardened condition and to a material, such asbar stock, for the production of such articles.

Attempts have been made to provide the trade with hard machine elementsmade from a bar stock of tough, high strength steel capable of beingfinished directly to final and accurate dimensions and of being heattreated to relatively high hardness without substantially distorting orotherwise warping out of shape. The problem of distortion isparticularly important in the manufacture of gears, especiallyautomotive gears. In order for gears to run quietly in service, it isessential that they pass through the heat treating operations with theminimum amount of change in size and shape. It is frequently found afterheat treatment that gears are not circular, that they have warped orthat they have increased or decreased in diameter. These shapeirregularities and variations are generally attributed to the heatingand quenching operations employed in the hardening heat treatment. Oneof the remedies suggested to overcome this disadvantage has been tosimplify the heat treatment of the gears. While this suggestion helpedto a certain extent in alleviating the condition, gears still had to beproduced with a sutficient oversize so as to allow for dimensionalvariation due to distortion which had to be corrected by grinding andmachining. Although attempts were made to overcome the foregoingdifficulties and other disadvantages, none, as far as we are aware, wasentirely successful when carried into production on a commercial andindustrial scale.

In searching for a solution to the above-described problem, it occurredto us that a nickel-aluminum dispersionor age-hardening steel might beemployed to overcome the foregoing difliculties encountered in producinggears. However, it was found that while this steel could be employed inproducing articles of finished dimensions with minimum distortion, thesteel did not usually have the desired hardness and, furthermore, didnot have the" required toughness and/ or strength for gears. Generally,it is desired that the gear steel be capable of hardening to at least 42Rockwell C. It was found that in most instances, the nickel-aluminumsteel was generally brittle and could not be employed under conditionsinvolving sudden applications of stress such as occur in tractor gearsand other automotive gears. For example, it was found that While anickel-aluminum steel containing about nickel and about 2% aluminumcould be heat treated and aged without substantially distorting, thesteel did not have adequate hardness and also did not have the requiredtoughness. Generally speaking, the steel was found to be too brittle andto have inferior resistance to impact stresses such as encountered ingears.

It has now been discovered that a hardened machine element, such as agear, a die, etc., having high strength combined with relatively highhardness and toughness can be produced directly from bar stock of aspecial dispersion-hardening steel to its finished dimensions withoutsubstantially distorting or warping after hardening by heat treatment.

It is an object of the present invention to provide a machine elementhardened to at least about 42 Rockwell C without substantiallydistorting or warping out of shape.

Another object of the invention is to provide a special machine elementbar stock made of a dispersion hardenable steel capable of being heattreated without exces-. sive distortion to a hardness of at least about42 Rockwell C combined with improved toughness.

The invention also contemplates providing improved machine elements,such as gears, dies, etc., which in use are subjected to wear and heavystatic and impact stresses.

Other objects and advantages will become apparent from the followingdescription.

Generally speaking, the present invention contemplates a hardenedmachine element made of a special dispersionhardenable steel hardened byheat treatment to a hardness of at least about 42 Rockwell C withoutsubstantially distorting or warping out of shape. The present inventionis based on the discovery that machine elements made of nickel-aluminumsteels have an improved combination of physical properties, particularlyimproved hardness in combination with high strength properties, improvedtoughness and improved resistance to impact, when the steel contains incombination with controlled amounts of nickel and aluminum critical andcontrolled amounts of the elements chromium and molybdenum. The steelcontemplated by the invention is unique in that it can be hardened byutilizing an austenitizing treatment, a tempering treatment and a lowtemperature aging treatment to produce the required hardness in combina-'tion with improved toughness and impact resistance without encounteringexcessive distortion or warping.

In general, the steel provided by the invention for use in machineelements contains as critical and essential elements about 3.5% to 6%nickel, about 1.5% to 2.5% aluminum, about 0.4% to 1.25% chromium, about0.2% to 0.3% molybdenum and about 0.18% to 0.3% carbon the balance ofthe composition being essentially iron. It is preferred for optimumphysical properties that the steel contain, together with the essentialelements chromium and molybdenum, vanadium in amounts not exceeding0.15%, the vanadium content being preferably at least about 0.05%. Inproducing the steel within the foregoing composition range, it isessential that the carbon content be correlated to the nickel andaluminum contents expressed stoichiometrically by the formula NiAl.Thus, when the NiAl content of the alloy falls within the range of about4.5% to 5.5%, the carbon content falls Within the range of about 0.25%to 0.30%. Likewise, when the NiAl content of the steel is within therange of about 5.5% to 7.5%, the carbon content is within the range ofabout 0.18% to 0.25%.

The machine elements provided by the present invention, such as gears,dies, etc., and made of the steel described herein are characterized bythe following improved properties and characteristics: adequate strengthand hardness to resist wear and abrasion together with suflicientresistance to failures resulting from stress con centrations asevidenced by relatively high notched impact strength. The machineelements contemplated by the invention may be employed at elevatedtemperatures up to about 1100 F. Although the temperature in service mayoccasionally exceed 1100 F. for short periods. of

time, such service should not be too prolonged as itcauses decrease inhardness.

As has been indicated hereinbefore, it is preferred foroptimum physicalproperties that all three of the elements a chromium, molybdenum andvanadium be present in amounts ranging from about 0.4% to 1.25%chromium, about 0.2% to 0.3% molybdenum and about 0.05% to 0.15%vanadium. It is also preferred that the steel contain silicon andmanganese, each in amounts up to about 1%. A preferred embodiment of asteel especially suitable as machine element bar stock contains about 5%nickel, about 2% aluminum, about 0.22% carbon, about 0.5% chromium,about 0.25% molybdenum, about 0.1% vanadium, about 0.25% silicon, about0.35% manganese, and the balance essentially. iron. The expression thebalance or the balance essentially as applied herein to iron does notexclude the presence of other elements in amounts which do not adverselyaffect the properties of the alloy. Thus, as mentioned hereinbefore,silicon and manganese may be present in the steel provided by theinvention, each in amounts not exceeding 1% of the total composition. Ofcourse, other elements may be present in the steel as a result of theuse of steel scrap in making up a charge, as a result of the use ofmaster addition alloys,

from the use of deoxidizers, degasifiers, purifiers and the like duringprocessing, etc. Examples of other elements which may be present withoutsubstantially adversely affecting the properties of the steel employedin producing bar stock for the machine elements provided by the inven- 2tion include up to 0.1% copper, up to 0.02% magnesium, up to 0.03%titanium, up to 0.01% calcium, up to 0.05% of phosphorus and sulfur,etc., the total amounts of such elements, including silicon andmanganese, usually not exceeding about 2.5% of the steel composition.The iron content of the steel may range from about 87% iron up to about94%.

By maintaining the nickel-aluminum steel within the composition limitsindicated hereinbefore, optimum hardness combined with toughness andhigh strength can be assured for machine elements produced from barstock thereof by employing a controlled heat treatment. This heattreatment comprises first subjecting the steel stock to a preliminarytreatment consisting of hardening by quenching or rapidly cooling thesteel from above the critical temperature (i. e., an austenitizingtemperature) followed by tempering at a temperature just below thecritical temperature and rapidly cooling. The thus-treated material isthen fabricated by hobbing, milling, grinding and the like into amachine element, such as a gear, hav- 7 ing the desired finaldimensions. The machine element is thereafter aged to the requiredhardness by heating at a temperature below the tempering temperature.The purpose of heating the steel stock above the critical temperatureand rapidly cooling it is to harden it completely by a formingmartensite. The purpose of the second heating or tempering treatment isto dissolve the age-hardening constituent associated with the nickel andaluminum contents and to fully temper the martensite and thereby put thesteel stock or blank in a relaively soft condition so that it can befinish machined to the desired final dimensions of the machine element,for example, a gear, being produced. The article is then aged ordispersion hardened by heating at the lower temperature. The use of thislower temperature enables the production of hardened gears and intricatedies of close tolerance without excessive distortion and with animproved combination of properties, including high strength combinedwith high toughness and impact resistance.

The high temperature or austenitizing treatment mentioned hereinbeforemay be conducted over the range of 1600 F. to 1750 F. for about 1 hourto 2 hours followed by'rapid cooling, such as, for example, by oilquenching. The steel stock'or blank may then be tempered by heating overthe range of about 1200 F. to 1275" F., but never above the Acitemperature of the steel, for about 1 hour to about 4 hours andthereafter rapidly cooled. The aging treatment may be conducted at atemperature from about 950 F. to 1100 F. for about 1 hour to 24 hours.Generally, when aging the steel to a hardness of at least 42 Rockwell Cover the temperature range of 950 F. to 1100 F., the time of heating atthe aging temperature is higher the lower the temperature and viceversa. Thus, at 950 F. the aging time would preferably range from about2 hours to 24 hours. At 1000 F., the desired hardness would preferablybe achieved by using times ranging from about 1 hour to 16 hours. At1050 1 the desired hardness can be achieved by aging from about 1 hourto 12 hours. At i100 F., only a short time would be required to achievethe desired age hardness, e. g., about one-half or one hour, etc., aslonger times, e. g., 2 hours or longer, tend to produce overaging orsoftening to below 42 Rockwell C.

In evaluating the suitability of a material for a machine element, thephysical properties generally relied upon include tensile strength,toughness or resistance to impact determined by the Charpy keyholeimpact test, hardness in terms of the Rockwell C numbers, etc. When, inaccordance with the invention, the nickel-aluminum steel employed in theproduction of a machine clement contains the two essential elementschromium and molybdenum and is hardened in the manner describedhereinbefore, unexpectedly improved properties are obtained which aresuperior to those obtained in a similar steel which does not contain orwhich is deficient in these elements. Generally, the steel provided bythe invention in the hardened state will have a high tensile strength ofat least about 190,000 p. s. i. (pounds per square inch) and a hardnessof at least 42 Rockwell C combined with a consistently higher level ofCharpy keyhole impact values which usually are at least about 5 footpounds.

For the purpose of giving those skilled in the art a betterunderstanding of the invention and a better appreciation of theadvantages of the invention, the following illustrative examples aregiven:

Example I A steel forged bar embodying the present invention wasproduced which contained about 4.97% nickel, 2.03% aluminum, 0.22%carbon, 0.49% chromium, 0.26% molybdenum, 0.095% vanadium, 0.18%silicon, 0.31% manganese and the balance essentially iron (hteel No. 1).The nickel and aluminum contents in the steel were sufficient to providea stoichiometric equivalent of about 6.45% NiAl. The bar stock of thesteel was austenitized at a temperature of about 1650" F. for about onehour followed by oil quenching and then solution treated at about 1275F. for about one hour followed by quenching in water. Finished machinedtest pieces were produced from the bar and aged variously from aboutonehalf hour to eight hours at temperatures ranging from about 950 F. to1100 F. The foilowing properties were obtained after aging It will benoted that the steel bar when aged over the temperature range of 950 F.to 1100 1 exhibited a hardness of at least 43 Rockwell C, ranging to ashigh as 46 Rockwell C. The tensile strength averaged over 200,000 p. s.i., while the Charpy impact values were generally in excess of 5 footpounds and averaged about 9 foot pounds. It was found that when the agintemperature was not lower than about 1000 F. or more, preferably notlower than about 1050 F., the level of properties was particularly high,especially with regard to impact resistance. The steel described in thisexample is very satisfactory for use as bar stock to produce a machineelement, for example, a gear, in accordance with the invention.

Example I] Another illustrative steel within the scope of the inventionwhich was found suitable for use as bar stock in the production ofmachine elements is one containing about 4.98% nickel, 2.0% aluminum,0.21% carbon, 0.44% chromium, 0.25% molybdenum, 0.28% silicon, 0.38%manganese, and the balance essentially iron (Steel No. 2). Theequivalent NiAl content of Steel No. 2 was about 6.35. This steel wastested as described for Example I except that it was austenitized at1700 F. for about one hour and quenched in oil and then solution treatedfor about one hour at 1275 F. followed by quenching in water. The finishmachined specimen pre pared from the thus-treated bar aged to at leastabout 42 Rockwell C hardness and exhibited high tensile strengthcombined with adequate toughness in the aged condition. There is little,if any, distortion after age hardening and bar stock made of this steelis suitable for use in machine elements.

For the purpose of better illustrating the advantages of the invention,a series of comparative tests were conducted with a group ofnickel-aluminum dispersion, hardening steels having compositions outsidethe invention. The compositions of these steels are illustrated in thefollowing schedule:

be noted that the steels within the invention are characterized by hightensile strength in combination with a high reduction of area of over40% and a Keyhole Charpy impact of over foot pounds and at least 8 footpounds and as high as 10 foot pounds. On the other hand, the steelsoutside the scope of the invention (A to E, inclusive) exhibited a muchlower order of reduction of area ranging from 1 to about 26% and a lowerorder of Keyhole Charpy impact not exceeding 4.5 foot pounds. Thecomparative data show clearly that molybdenum in an amount of about0.25% and vanadium in an amount of about 0.20%, each whether alone ortogether (Steels A to D), were insufiicient to produce adequatetoughness with a hardness of at least 42 Rockwell C. Of the steelswithin the scope of the invention, Steel 1, which contained all three ofthe elements chromium, molybdenum and vanadium, exhibited optimumproperties as compared to the steel in which only chromium andmolybdenum were employed in accordance with the invention.

Results have indicated that the tendency toward brittleness exhibited bythe nickel-aluminum steel outside the scope of the invention appears tobe associated with the retention of a ferritic phase after theaustenitizing treatment. Tests have indicated that the amount of theretained ferritic phase appears to be a function of the aluminum contentof the steel. For example, in a steel containing about 4.5% nickel, ithas been found that the amount of ferrite increases from about 1% withan aluminum content of about 1.16% to a ferrite content of about 85%with an aluminum content of about 4.15%.

This is illustrated by the following data for a steel con- Per- I Per-Per- Per- Per- Per- Per- Per- Per- Per- Steel cent cent cent cent centcent cent 7 cent cent cent Ni Al N 1A1 0 Cr Mo Si Mn Fe 5. 43 2. 20 6.98 0.21 0. 26 0.16 0.34 Bal. 4.93 2.06 6. 56 0.22 0.25 0.28 0.37 Bal. 5.32 2.13 6. 78 0. 21 0.26 0.20 0 11 0. 23 Bal. 5. 41 2. 38 7. 56 0.200.20 0. 12 0.31 Bal. 5. 77 2. 23 7.10 0.22 0. 24 0. Bal.

Comparative data illustrating the advantages of the invention are givenin the following schedule which compares the steels of Examples I and 11provided by the invention with the aforementioned steels outside theinvention.

All of the steels, with the exception of Steel E, were austenitized forone hour at a temperature within the range of 1650 F. to 1750" F.followed by quenching in oil. These same steels were then given asolution heating for one hour at 1275 F. followed by quenching in waterand thereafter aged at a temperature within the range of about 1025 F.to 1050 F. for about two to eight hours. Steel E, on the other hand, wasaustenitizcd for one hour at 1600 F. and then oil quenched followed by asolution heating for one hour at 1275 F. followed by quenching in water.This steel was then age hardened at 950 F. for about 24 hours. It willbe noted from the comparative data that while all the steels had an agehardness of at least about 42 Rockwell C, the best and optimumcombination of properties was obtained by Steels Nos. 1 and 2 within thescope of the invention. It will taining nickel, aluminum and carbon withthe balance essentially iron.

Steel Percent Percent Percent Percent Percent Ni Al NiAl C Ferrite 5 Itwill be noted from the above tabulation that only a small amount ofaluminum in the neighborhood of about 1% can be tolerated in avoidingthe presence of harmful amounts of ferrite in a steel having an adequateamount of nickel. However, Steel F could not be hardened to 42 0Rockwell C, but had a hardness of only 33 Rockwell C.

The presence of free ferrite in the other three steels greatly aifectedthe resistance of the steels to the Keyhole Charpy impact test. This wasevident by the results obtained on Steel E mentioned hereinbefore whichcontained about 2.23% aluminum. After being subjected to theaustenitizing treatment and tempered and aged to a hardness of 43Rockwell C, Steel E exhibited a Charpy impact value of only 2 footpounds and a reduction in area of only 1% for a low strength value of187,000

70 p. s. i. The addition of the essential elements chromium 75 ness incombination with high hardness, high strength properties and highreduction in area.

As has been stated hereinbefore, it is essential in producing thespecial nickel-aluminum steel provided by the invention for use as amachine element that the nickel and aluminum contents expressedstoichiometrically by the formula NiAl range from about 4.5% to about7.5% NiAl. When the NiAl content is reduced below about 5%, andespecially below about 4.5%, the minimum Rockwell C hardness of 42 ishardly attained after aging, even when the composition is bolstered bysutlicient alloy additions to inhibit retention of ferrite during theharden- Tests have indicated it is essential that the carbon content becorrelated to the NiAl content of the steel in. order to obtain theresults of the invention. Thus, when the NiAl content ranges from about4.5% to 5.5 the correlated carbon content should range from about 0.25%to 0.3%. Likewise, when the NiAl content of the steel ranges from about5.5% to 7.5%, it is essential that the correlated carbon content rangefrom about 0.18% to 0.25%.

In order to achieve the minimum age hardness of at least 42 Rockwell Ccontemplated by the invention, it has been found that the solutionquench hardness prior to aging should range from about 25 to 32 RockwellC. Generally, the higher the solution hardness the higher will be theaged hardness. The increment of hardness obtained by aging tends to belower the higher the solution hardness before aging. This relationshipis illustrated by the following Rockwell C hardness determinations on anickel-aluminum steel containing about 6% to 7% NiAl and about 0.20% to0.25% carbon:

The foregoing data confirm that when the solution quench hardness isabout 25 Rockwell C, an age hardness of at least about 42 Rockwell C isobtained. able for the solution quench hardness prior to aging to exceed32 Rockwell C as hardnesses in excess of 32 Rockwell C make it diiiicultto machine the steel to the final dimensions of the machine elementprior to aging and also adversely affect the toughness of the steel inthe finally aged condition. When the steel contains 6% to 7% and higherof NiAl together with moderate additions of the essential elementschromium and molybdenum, with or without vanadium, in accordance withthe invention, a solution quench hardness of up to 32 Rockwell C isreadily obtainable. When either of the essential elements chromium andmolybdenum, or both, is deficient in the amount stated hereinbefore orabsent, even though 6% to 7% NiAl be present, two undesirable effectsare generally indicated in the final product: (1) lack of full hardnessafter aging and (2) noticeable brittleness after aging.

It has been found that in order to insure high toughness with highhardnesses in excess of 42 Rockwell C, the steel provided by theinvention should have a solution quench hardness of the order of about30 Rockwell C or greater and should be aged at a temperature of about1050 F. When the steel contains about 2% aluminum or more and has a highNiAl content, c. g., above 6% NiAl, it is preferred that theaustenitizing temperature employed in the preliminary heat treatment beof the order of about 1700 F. in order to insure optimum properties inthe aged condition.

In producing the machine elements contemplated by the present invention,the special steel or bar stock made It is not desirthereof may beproduced in the conventional manner well known to those skilled in theart. Thus, the steel may be produced in an electric furnace. Likewise,the charge may be composed of the various constituents either inelemental form or as special master alloys or ferro-alloys. Of course,scrap may also be used in the charge as is well known. Similarly, themolten metal may be treated in the conventional manner to produce soundand clean metal for poured ingots. The ingots can then be mechanicallworked in a conventional manner into bar stock, such as by forging androlling.

As pointed out hereinbefore, the present invention is particularlyapplicable to the production of hardened machine elements, such asgears, dies, cams, hydraulic valve seats and valve stems and otherhydraulic valve parts. etc. These machine elements have the commoncharacteristic that they all require a high order of hardness to resistwear and distortion which heretofore could only be obtained by employinghigh temperature hardening heat treatments together with laborious andexpensive tooling of the hardened steel to correct distortion orundesirable surface defects produced in the high temperature hardeningoperation. illustrative examples of gears which may be produced inaccordance with the present invention include tractor gears, automobilegears, reduction gears, transmission gears of various kinds, etc.Illustrative examples of dies include die-casting dies for eastingmolten aluminum and zinc, which dies are designed not to heat in serviceto temperatures high enough, for

xampi over 1100 F., to cause overaging and softening.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understod that modifications andvariations may be resorted to Without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

We claim:

1. A hardened gear which in use is subjected to wear and heavy staticand impact stresses, said element being comprised of a heat treatedsteel containing about 3.5% to 6% nickel, about l.5% to 2.5% aluminum,about 0.4% to 1.25% chromium, about 0.2% to 0.3% molybdenum, about 0.05to 0.15% vanadium, up to about 1% silicon, up to 1% manganese, and about0.18% to 0.3% carbo the carbon content being correlated to the nickeland aluminum contents in the alloy expressed stoichiometrically by theformula NiAl, such that when the NiAl content of the steel is within therange of about 4.5% to about 5.5%, the carbon content is within therange of 0.25% to 0.30% and when the NiAl is within the range of about5.5% to 7.5%, the carbon content is within the range of about 0.18% to0.25%, the balance of said steel being essentially iron.

2. A hardened machine element which in use is subjected to wear andheavy static and impact stresses, said element being comprised of a heattreated steel containing about 3.5 to 6% nickel, about 1.5 to 2.5%aluminum, about 0.4% to 1.25% chromium, about 0.2% to 0.3% molybdenum,about 0.05% to 0.15% vanadium, and about 0.18% to 0.3% carbon, thecarbon content being correlated to the nickel and aluminum contents inthe alloy expressed stoichiornetrically by the formula NiAl,

such that when the NiAl content of the steel is within the range ofabout 4.5% to 5.5%, the carbon content is within the r of about 0.25% to0.30% and when the NiAl is within the range of about 5.5% to 7.5%, thecarbon content is within the range of about 0.18% to 0.25%, the balanceof said steel being essentially iron.

3. A hardened machine element which in use is subcted to wear and heavystatic and impact stresses, said element being comprised of a heattreated steel containing about 3.5% to 6% nickel, about 1.5% to 2.5%aluminum, about 0.4% to 1.25% chromium, about 0.2%

to 0.3% molybdenum, up to about 0.15% vanadium, up to about 1% silicon,up to about 1% manganese, and about 0.18% to 0.3% carbon, the carboncontent being correlated to the nickel and aluminum contents in thealloy expressed stoichiometrically by the formula NiAl, such that whenthe NiAl content of the steel is within the range of about 4.5 to 5.5the carbon content is Within the range of about 0.25% to 0.30%, and whenthe NiAl is within the range of 5.5% to 7.5%, the carbon content iswithin the range of about 0.18% to 0.25 the balance of said steel beingessentially iron.

4. A hardened machine element which in use is subjected to wear andheavy static and impact stresses, said element being comprised of a heattreated steel containing about 3.5% to 6% nickel, about 1.5% to 2.5%aluminum, about 0.4% to 1.25 chromium, about 0.2% to 0.3% molybdenum, upto about 1% silicon, up to about 1% manganese, and about 0.18% to 0.3%carbon, the carbon content being correlated to the nickel and aluminumcontents in the alloy expressed stoichiometrically by the formula NiAl,such that when the NiAl content of the steel is within the range ofabout 4.5% to 5.5 the carbon content is within the range of about 0.25%to 0.30% and when the NiAl is within the range of about 5.5% to 7.5%,the carbon content is within the range of about 0.18% to 0.25%, thebalance of said steel being essentially iron.

5. A hardened die-casting die which in use is subjected to wear andheavy static and impact stresses, said element being comprised of a heattreated steel containing about 3.5% to 6% nickel, about 1.5% to 2.5%aluminum, about 0.4% to 1.25% chromium, about 0.2% to 0.3%

molybdenum, about 0.05% to 0.15% vanadium, up to about 1% silicon, up toabout 1% manganese, and about 0.18% to 0.3% carbon, the carbon contentbeing correlated to the nickel and aluminum contents in the alloyexpressed stoichiometrically by the formula NiAl, such that when theNiAl content of the steel is within the range of about 4.5% to 5.5 thecarbon content is Within the range of about 0.25 to 0.30% and when theNiAl is within the range of 5.5 to 7.5 the carbon content is within therange of about 0.18% to 0.25 the balance of said steel being essentiallyiron.

6. A dispersion-hardenable steel suitable for the production of hardenedmachine elements such as gears, dies and other articles which in use aresubjected to wear and heavy static and impact stresses which comprisesabout 3.5 to 6% nickel, about 1.5% to 2.5% aluminum, about 0.4% to 1.25%chromium, about 0.2% to 0.3% molybdenum, and about 0.18% to 0.3% carbon,the carbon content being correlated to the nickel and aluminum in thealloy expressed stoichiometrically by the formula NiAl, such that whenthe NiAl content of the steel is within the range of about 4.5% to 5.5%, the carbon con tent is Within the range of about 0.25% to 0.30% andwhen the NiAl is Within the range of 5 .5 to 7.5%, the carbon content isWithin the range of about 0.18% to 0.25%, the balance of the steel beingessentially iron.

References Cited in the file of this patent UNITED STATES PATENTS

1. A HARDENED GEAR WHICH IN USE IS SUBJECTED TO WEAR AND HEAVY STATICAND IMPACT STRESSES, SAID ELEMENT BEING COMPRISED OF A HEAT TREATEDSTEEL CONTAINING ABOUT 3.5% TO 6% NICKEL, ABOUT 1.5% TO 2,5% ALUMINUM,ABOUT 0.4% TO 1.25% CHROMIUM, VANADIUM, UP TO ABOUT 1% DENUM, ABOUT 0.05TO 0.15% VANADIUM, UP TO ABOUT 1% SILICON, UP TO 1% MANGANESE, AND ABOUT0.18% TO 0.3% CARBON, THE CARBON CONTENT BEING CORRELATED TO THE NICKELAND ALUMINUM CONTENTS IN THE ALLOY EXPRESSED STOICHIOMETRICALLY BY THEFORMULA NIAL, SUCH THAT WHEN THE NIAL CONTENT OF THE STEEL IS WITHIN THERANGE OF ABOUT 4.5% TO ABOUT 5.5%, THE CARBON CONTENT IS WITHIN THERANGE OF 0.25% TO 0.30% AND WHEN THE NIAL IS WITHIN THE RANGE OF ABOUT5.5% TO 7.5%, THE CARBON CONTENT IS WITHIN THE RANGE OF ABOUT 0.18% TO0.25%, THE BALANCE OF SAID STEEL BEING ESSENTIALLY IRON.